How Radiant Barrier Works
Definitions:
- Radiant Heat: Heat transferred by radiation in the form of waves which travels through space. Radiant Heat is absorbed or reflected by the first solid object it encounters.
- Radiant Barrier: a material which blocks/reflects radiant heat. Made from reflective materials like aluminum, they typically block 95-97% of the radiant heat.
- Emissivity: the amount of heat which is "emitted" or radiated off of a surface to the surrounding air.
- Reflect: to bend back; to give a backward turn to; especially, to cause to return after striking upon any surface; as, a mirror reflects rays of light.
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There are two properties on which radiant barriers work: Reflectivity and Emissivity. First, the aluminum is reflective on the hot side, reflecting some of the heat back from where it came. Second, and most importantly, aluminum has a low emissivity of between 0.03 and 0.05. This means that only 3% to 5% of the heat is emitted to the air on the cold side. In order to benefit from both of these properties, the radiant barrier must be double sided (aluminum on both sides) and installed so that there is an air space or low density material (like insulation) on both sides.
In an attic with no radiant barrier, radiant heat from the hot roof travels down through the open space and is absorbed by attic insulation, ductwork, and air handlers.
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Radiant Barrier Keeps Heat Out During the Summer |
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In the summer, typically the largest source of heat gained by your home or building is radiant heat energy. A large amount of this heat comes through the roof and ceiling. If you have spent any time in an attic on a summer day you understand this completely. The roof and walls of your home absorb the radiant heat coming from the sun. This heat moves by conduction towards the interior until it reaches an air space such as the attic or drainage plane behind your outer veneer. At this point it radiates across that space. If you have Radiant Barrier installed next to that air space, most of this radiated heat is reflected back towards the outside. Without Radiant Barrier installed, this radiated heat is absorbed by the interior surfaces of your home.
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Illustration showing summer savings
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In fact, regular insulation does little to reflect radiated heat; it just absorbs and holds this heat. In addition, HVAC equipment located in an attic will absorb attic heat and transfer it into the house. A properly installed Radiant Barrier can block up to 97% of this radiant heat, saving you money year after year. |
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Radiant Barrier Keeps Heat In During the Winter |
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In the winter, heat conducts through your ceiling, walls and floor and is lost by radiation and convection. Radiant Barrier installed in the attic will reflect much of the radiant heat back towards the source. Radiant Barrier used as a house wrap can reduce radiant and convective heat losses through the walls. When heat is lost through the ceiling, walls and floor, your home's heater works to reheat the space. Properly installed Radiant Barrier can reduce this wasted energy by reflecting much of the heat back towards the interior of the building, keeping your home warmer and reducing your heating bills. As the cost of natural gas and electricity continues to increase, payback times decrease. If you are able to install Radiant Barrier yourself, payback times can be less then one year.
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Illustration showing winter savings
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Proceed to Selecting the Proper Material
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